Photodynamic action of amino substituted hypocrellins: EPR studies on the photogenerations of active oxygen and free radical species

A novel method has been employed to prepare 2-butylamino-2-demethoxy hypocrellin A (BADMHA) and 3-butylamino-2-demethoxy hypocrellin B (BADMHB). Both compounds exhibit stronger absorption at the phototherapeutic window (600-900: nm). The spin trapping and spin counteraction studies have shown that they are both efficient generators of the active oxygen (O-1(2), O-2(.-)) in the aerobic condition. Under the anaerobic condition they generate non-oxygen free radical (semiquinone radical anion), and the active oxygen mechanism of photosensitization can be converted into cion-oxygen free radical mechanism with the depletion of oxygen. The quantum yields of O-1(2) generation of BADMHA and BADMHB are 0.46 and 0.44, respectively. Both are lower than those of their parent compounds HA and HE. But the productions of superoxide anion are enhanced significantly compared with HA and HE, indicating they are both favorable Type I phototherapeutic agents. (C) 2000 Elsevier Science S.A. All rights reserved.